100,000-gallon sewage spill reported in Kentfield

A foul odor in Kentfield led to the discovery of a break in a sewer pipe on Monday.

Ross Valley Sanitary District General Manager Greg Norby estimates that approximately 100,000 gallons of wastewater spilled into surrounding soil near Tamalpais Creek where it crosses under Evergreen Drive.

Norby said Tamalpais Creek is not currently flowing so it is unlikely the wastewater reached Corte Madera Creek, which connects with Tamalpais Creek.

The spill was caused by a separation at a sewer pipe joint where clay pipe is joined with a polyvinyl chloride plastic pipe as it crosses under Tamalpais Creek.

According to a press released issued by the district, "This separation allowed wastewater to seep in to the ground with some of it resurfacing in static pools in the creek bed."

Ammonia testing of the pools indicates the wastewater did not reach Corte Madera Creek, but testing will continue under the direction of Marin County Environmental Health Services.

Norby said the estimate of wastewater spilled is based on measurements of the rate of flow escaping from the pipe and the assumption that the break in the pipe occurred about two weeks ago. Norby said it takes a number of days after a spill first occurs before odors become noticeable to neighbors.

"It takes about that long for it to go septic and start generating the odors," Norby said.

Repairs to the pipe were completed on Monday. But Norby said the district is consulting with the California Department of Fish and Wildlife and the U.S. National Marine Fisheries Service before vacuuming up any of the static pools in Tamalpais Creek that were contaminated by the spill. Norby said some minnnow-sized fish have been spotted in the pools, and he wants to make sure the fish aren't salmon or another other species of concern.

Norby said the area of the pipe where the break occurred was inspected in 2011 and no defect was spotted at that time. This area of pipe was not on the district's long list of sections in need of urgent repair, Norby said.